This invention generally relates to a system and method for providing regulated flow of oxygen, including for a pilot or cockpit crew member on-board an aircraft. The invention more particularly relates to a system and method for ensuring that oxygen gas suitable for breathing is rapidly and intermittently available to a pilot or cockpit crew member on-board an aircraft including during an aircraft's descent. Components of the system include oxygen generators.
Conventional systems and methods for supplying oxygen to an aircraft pilot or cockpit crew member rely on gaseous oxygen contained in cylinders that are stored on-board the aircraft and delivered to pressure and/or flow regulator devices.
There are disadvantages to relying entirely on either a pressurized cylinder of oxygen enriched gas or a chemical oxygen generator. Pressurized cylinders of oxygen enriched gas add significant weight to an oxygen supply system and contribute to its hazard potential by providing an ever-present risk of combustion. Added weight increases fuel costs. Oxygen from pressurized cylinders of gas may be distributed from one or more sources within a distribution network of an aircraft or individual cylinders may be provided for each pilot and cockpit crew member. In either case, given the limited space of an aircraft, oxygen from the cylinders is typically not far from components of the aircraft's illumination system increasing the hazard potential. For example, individual cylinders or outlets of a distribution network above the seats are near the lights. Chemical oxygen generators decrease this hazard potential and reduce the weight of continuously storing pressurized gaseous cylinders but have limited applications. For example, chemical oxygen generators are designed to be usable only a single time for shorter flights (e.g. under about 22 minutes) and their applicability may further depend upon the terrain of the flight path. The need to refill pressurized cylinders and to replace single use chemical oxygen generators increases the maintenance costs for aircraft oxygen supply systems.
A system is known that utilizes molecular sieve bed and/or permeable membrane technology, to produce first, oxygen for use for breathing by an aircrew, and second, nitrogen for use as an inert environment in the fuel tanks of an aircraft. However such systems still require the provision of compressors for both the oxygen, in order that the oxygen can be delivered at an appropriate pressure for breathing, and for the nitrogen. Also, the concentration of oxygen which can be produced is restricted by virtue of the nature of the conventional on-board oxygen generator (OBOG) device technology which is used.
Pressure swing adsorption (PSA) technology is based on the principle that gases under pressure are generally attracted to solid surfaces upon which the gases are adsorbed. Higher pressure results in greater gas adsorption. When the pressure is reduced or swings from high to low, gas is released or desorbed. Gaseous mixtures may be separated through pressure swing adsorption (PSA) because different gases tend to be adsorbed or attracted to different solid materials to varying degrees. Accordingly, when the pressure is reduced gases that are less strongly attracted to the solid materials will be desorbed first to form an outlet stream. After the bed of solid material to which gases are adsorbed reaches its capacity to adsorb, pressure is further reduced to release even the more strongly attracted gases. As applied to an on-board oxygen generator (OBOG), engine bleed air is typically fed into the pressure swing adsorption (PSA) device, the nitrogen component of air is adsorbed to a bed of solid material more strongly than the oxygen component of air, and an outlet stream of enriched oxygen is produced. This is similar to the process used in portable oxygen concentrators for emphysema patients and others who require oxygen enriched air to breathe.
On-board oxygen generators (OBOG) based on pressure swing adsorption (PSA) technology are dependent upon compressed air. On an aircraft this compressed air is typically available as engine bleed air having pressure in the range of 30 to 40 psig and at a temperature in the range of 320 to 380° F. However, in the event engine bleed air or compressed air from an alternative source is not readily available, compressors may be used to pressurize air sufficiently that it is suitable to be received by a pressure swing adsorption (PSA) type on-board oxygen generator (OBOG).
Adsorbents for pressure swing adsorption (PSA) systems must have the ability to discriminate between two or more gases demonstrating selective adsorption. Suitable adsorbent materials for ppressure swing adsorption (PSA) systems are usually very porous materials selected for their large surface areas, for example activated carbon, silica gel, alumina and zeolites. The gas adsorbed on these surfaces may consist of a layer only one or at most a few molecules thick. Adsorbent materials having surface areas of several hundred square meters per gram enable the adsorption of a significant portion of the adsorbent's weight in gas. The molecular sieve characteristics of zeolites and some types of activated carbon called carbon molecular sieves serve to exclude some gas molecules based on size, in addition to the differential adsorption selectivity for different gases.
Oxygen for breathing generated by on-board oxygen generator (OBOG) devices typically is not rapidly available due to the required cycling through membranes. While ceramic oxygen generator (COG) devices typically are superior to molecular sieve oxygen generator (MSOG) devices based upon an ability to provide purer or more highly concentrated oxygen-enriched gas at pressure, oxygen from ceramic oxygen generator (COG) devices is also not rapidly available due to the high temperature requirement necessary for oxygen generation from such devices. It would be desirable to provide a system that leverages the advantages of on-board oxygen generators (OBOG), including ceramic oxygen generator (COG) devices incorporating existing solid electrolyte oxygen separation (SEOS) technology and molecular sieve oxygen generator (MSOG) devices incorporating pressure swing adsorption (PSA) technology, without sacrificing availability of breathable oxygen gas in the short-term during descent or upon an emergency situation arising by integrating other components capable of providing high purity oxygen in the short-term.
It would also be desirable to provide a system incorporating a molecular sieve oxygen generator (MSOG) device that utilizes pressure swing adsorption (PSA) technology to supply sufficiently oxygen enriched air at holding altitudes below 30,000 feet. The ability to rely on molecular sieve oxygen generator (MSOG) devices to supply oxygen below 30,000 feet may also reduce the cost of electricity and heating for the ceramic oxygen generator (COG) devices that produce more highly enriched oxygen gas (about 99% pure) required for altitudes of 30,000 feet and up.
It would further be desirable to provide a system that includes a controller for managing the supply of oxygen from the various sources in the system to ensure a prompt, rich supply of oxygen is available, to maximize efficiency of oxygen usage, and to recycle or store for future use gaseous products that are not needed in the short-term.
Heavy pressurized oxygen cylinders and single use chemical oxygen generators contribute to the maintenance costs of aircrafts reliant upon these oxygen sources. It would be highly advantageous to reduce reliance on pressurized gaseous oxygen cylinders and chemical oxygen generators by reserving their usage to emergency and descent situations before oxygen enriched gas from an on-board oxygen generator (OBOG) device is available.
Finally, it would be advantageous to conserve oxygen that is available or generated by providing oxygen to the masks of passengers or crew through a pulsed supplier with a feedback mechanism such that oxygen flow is only provided as needed. The present invention meets these and other needs.